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Title: Validity over time of self-reported anthropometric variables during follow-up of a large cohort of UK women
Authors: Wright FL; Green J; Reeves G; Beral V; Cairns BJ; for the Million Women Study Collaborators (incl. Canfell K)
Categories: Etiology - Resources and Infrastructure
Year: 2015
Journal Title: BMC Medical Research Methodology
Abstract: BACKGROUND: In prospective epidemiological studies, anthropometry is often self-reported and may be subject to reporting errors. Self-reported anthropometric data are reasonably accurate when compared with measurements made at the same time, but reporting errors and changes over time in anthropometric characteristics could potentially generate time-dependent biases in disease-exposure associations. METHODS: In a sample of about 4000 middle-aged UK women from a large prospective cohort study, we compared repeated self-reports of weight, height, derived body mass index, and waist and hip circumferences, obtained between 1999 and 2008, with clinical measurements taken in 2008. For self-reported and measured values of each variable, mean differences, correlation coefficients, and regression dilution ratios (which measure relative bias in estimates of linear association) were compared over time. RESULTS: For most variables, the differences between self-reported and measured values were small. On average, reported values tended to be lower than measured values (i.e. under-reported) for all variables except height; under-reporting was greatest for waist circumference. As expected, the greater the elapsed time between self-report and measurement, the larger the mean differences between them (each P < 0.001 for trend), and the weaker their correlations (each P < 0.004 for trend). Regression dilution ratios were in general close to 1.0 and did not vary greatly over time. CONCLUSION: Reporting errors in anthropometric variables may result in small biases to estimates of associations with disease outcomes. Weaker correlations between self-reported and measured values would result in some loss of study power over time. Overall, however, our results provide new evidence that self-reported anthropometric variables remain suitable for use in analyses of associations with disease outcomes in cohort studies over at least a decade of follow-up.
Division: Cancer Research Division
Funding Body: Funding for this study was provided by the Medical Research Council (grant MR/K02700X/1), Cancer Research UK (grant no. C570/A11692), and the NHS Cancer Screening Programme (reference no. R19220/CN002). Dr Cairns acknowledges support from the BHF Centre of Research Excellence, Oxford (British Heart Foundation grant RE/13/1/30181).
DOI: 10.1186/s12874-015-0075-1
Appears in Collections:Research Articles

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